1. Field of the Invention
The present invention relates to an optical disk recorder for recording television broadcast signals on an optical disk, and a method of writing signal to the optical disk.
2. Description of the Related Art
In the prior art, an optical disk recorder for recording television broadcast signals on an optical disk such as DVD (Digital Versatile Disk) has been put to practical use. Usually, such optical disk recorder comprises a back-end buffer (hereafter referred to as “BE buffer”) and a front-end buffer (hereafter referred to as “FE buffer”). The broadcast signals received by a tuner are output to an optical pickup as appropriately, while being sequentially buffered in the BE buffer and the FE buffer.
In the optical disk recorder, the broadcast signals are recorded in accordance with a video recording standard. Optical disks capable of recording, using the optical disk recorder, include those to which signals are rewritable. If signals are frequently rewritten to such rewritable optical disks, recorded and unrecorded areas are sometimes fragmented.
FIG. 4 schematically shows an example of such area-fragmented optical disk, in which an unrecorded area (A) and a further unrecorded area (B) exist, sandwiching a recorded area. FIG. 5A to FIG. 5C show time variations of buffer storage amount in the FE buffer, transfer rate from the BE buffer to the FE buffer, and write rate of the optical pickup, respectively, when video images are continuously recorded or written in the unrecorded area (A) and the unrecorded area (B) of the optical disk shown in FIG. 4. Since compressed and coded data alone are transferred between the BE buffer and the FE buffer of the optical disk recorder, the transfer rate between them is restricted to be lower as compared with those of e.g. so-called personal computers.
Initially, when the video recording starts, signals stored in the BE buffer are transferred to the FE buffer at a transfer rate Rt. The FE buffer has a threshold value (initial storage threshold value) M set therein which is smaller than the upper limit of its buffer capacity, so as to enable recovery by rewriting when a tracking error or a focusing error occurs due to e.g. vibrations applied to the optical disk recorder during writing of the signals. When the storage amount in the FE buffer reaches the threshold value M at time T11 due to the signal transfer from the BE buffer, the signals stored in the FE buffer are output to the optical pickup, and the writing is started. At this time, the signal transfer from the BE buffer to the FE buffer continues on. However, write rate Rw of the optical pickup is higher than the transfer rate Rt, so that the storage amount in the FE buffer gradually decreases, and becomes zero at time T12. Thereafter, the writing by the optical pickup is paused until the buffer storage amount reaches the threshold value M again. In this way, the broadcast signals are written to the optical disk in the optical disk recorder multiple times dividedly while being buffered by the BE buffer and the FE buffer.
As the video recording proceeds in this way, and the transfer, from the BE buffer to the FE buffer, of all the signals to be recorded or written in the unrecorded area (A) is completed at time T13, the transfer of the signals to the FE buffer temporarily ends. Since the optical pickup continues writing signals at the write rate Rw at this time as well (refer to FIG. 5C), the storage amount in the FE buffer abruptly decreases, and becomes zero at time T14, thereby ending the video recording in the unrecorded area (A). Thereafter, the optical pickup seeks to a position corresponding to the beginning of the unrecorded area (B), and then starts recording or writing in the unrecorded area (B).
Besides, an optical disk device is known which intermittently rotates an optical disk when the amount of information to be recorded or reproduced per unit time is less than a given threshold value (refer to e.g. Japanese Laid-open Patent Publication 2003-217227). A further known optical disk device selects a certain operation in accordance with a predetermined order of priority based on kinds of recording/reproducing operations so as to decide the operation to be performed next (refer to e.g. Japanese Laid-open Patent Publication 2002-203363). A still further known optical disk device sets the seek speed to low for normal recording, and switches the seek speed to high when the storage amount in a buffer exceeds a certain amount (refer to e.g. Japanese Laid-open Patent Publication 2003-281745).
However, the optical disk recorder in the prior art as first described above has the following problem. In it, there exists time interval ΔT between time T13 and time T14 during which only the writing is performed, so that the seek operation cannot immediately start at time T13 when the signal transfer is ended, causing the video recording to take a long time. Accordingly, it is required to store, in the BE buffer, broadcast signals received from time T13 to time T15 at which the signal transfer is resumed for writing in the unrecorded area (B). Hence, there is a possibility that the BE buffer overflows, causing video images and sounds to be interrupted. The above refers to the problem in the case of the video recording in the unrecorded area (A) and the unrecorded area (B) continuously as shown in FIG. 4 and FIGS. 5A to 5C. However, similar problem arises in the case of so-called “chasing playback” or simultaneous recording and reproduction, in which signals already recorded in the recorded area are reproduced while the recording in the unrecorded area (A) is performed. More specifically, in the case of the “chasing playback”, it is not possible to immediately start the seek operation and then the reproduction operation at time T13 when the signal transfer is ended.
Such problem cannot be solved by any one of the devices as disclosed in the above patent publications.